Liquid crystal displays perform display by making a displaying side substrate and a liquid crystal driving side substrate face to each other, enclosing a liquid crystal compound between the two to form a thin liquid crystal layer, and electrically controlling the liquid crystal alignment within the liquid crystal layer with the liquid crystal driving side substrate to change the amount of transmitted light or reflected light of the displaying side substrate selectively.
Such a liquid crystal display includes various driving methods such as the static driving method, the passive matrix, and the active matrix. In recent years, a color liquid crystal display using a liquid crystal panel of the active matrix or the passive matrix is rapidly getting in prevalence as a flat display for such as a personal computer or a portable information terminal.
FIG. 3 is one example of a liquid crystal display panel of the active matrix. A liquid crystal display 101 assumes the structure of being a color filter 1 serving as a displaying side substrate and a TFT array substrate 2 serving as a liquid crystal driving side substrate facing each other with a gap portion 3 of about 1 to 10 μm in between, and this gap portion 3 is filled with a liquid crystal L, and the surroundings thereof are sealed with a sealing material 4. The color filter 1 assumes the structure of a black matrix layer 6 formed into a predetermined pattern to shield the boundary portion between the pixels against light, a pixel portion 7 in which a plurality of colors (typically, three primary colors of red (R), green (G), and blue (B)) are arranged in a predetermined order to form each pixel, a protective film 8, and a transparent electrode film 9 are laminated on a transparent substrate 5 in this order from the side near to the transparent substrate.
On the other hand, the TFT array substrate 2 assumes the structure of being TFT elements aligned on a transparent substrate, and a transparent electrode film is disposed (not illustrated). Also, an alignment film 10 is disposed on the inner surface side of the color filter 1 and the TFT array substrate 2 facing thereto. Then, a color image is obtained by controlling the light transmittance of the liquid crystal layer that lies in the background of the pixels colored in each color.
Here, the thickness of the gap portion 3, i.e. the cell gap (the gap distance between the displaying side substrate and the liquid crystal driving side substrate) is no other than the thickness of the liquid crystal layer. Therefore, in order to prevent display mura such as color mura or contrast mura and to impart good display performances such as uniform display, fast responsiveness, high contrast ratio, and wide viewing angle to the color liquid crystal display, one has to maintain the cell gap to be constant and uniform.
As a method of maintaining the cell gap, a method in which numerous spherical or rod-shaped particles 11 made of glass, alumina, plastic, or the like and having a predetermined size are dispersed in the gap portion 3 as spacers; the color filter 1 and the TFT array substrate 2 are bonded; and a liquid crystal is injected is known. With this method, the cell gap is determined and maintained by the size of the spacers.
However, the method of dispersing particles in the gap portion as spacers involves various problems such as a tendency of the spacer distribution being deviated. As a method of solving these problems of the particulate spacers, columnar spacers 12 having a height corresponding to the cell gap in a region (non-display region) that is located on the inner surface side of the color filter 1 and overlaps with the position where the black matrix layer 6 is formed are begun to be formed, as illustrated in FIG. 4. The columnar spacers 12 have been formed within the region where the black matrix layer is to be formed, i.e. the non-display region, by applying a photosetting resin in a uniform thickness on a transparent substrate of a color filter and exposing and setting the obtained coating film in a pattern by photolithography.
In recent years, such a liquid crystal display has been rapidly increasing its display area. When the substrate area increases in this way, it will be difficult to adopt a mechanic press method that has been conventionally carried out in curing the sealing material and enclosing the liquid crystal, in view of ensuring the uniformity of the curing of the sealing material, problems of equipment, and the like. Therefore, it is now often carried out by the vacuum press method. However, with the vacuum press method, the load applied onto the cells is extremely small as compared with the mechanic press method, so that the liquid crystal that has been superfluously injected into the cell cannot be squeezed out. Typically, when the cells are assembled by mechanic pressing, they are sealed in a state in which a sufficient load is imposed on the cells, so that the columnar material will not depart from the opposing substrate even if the liquid crystal undergoes thermal expansion due to energization of the backlight or the like. However, when the cells are assembled by the vacuum press method, the load applied onto the cells is weak, so that the opposing substrate will depart from the columnar material when the liquid crystal undergoes thermal expansion. By this, the liquid crystal will be present in deviation in the lower part of the liquid crystal panel, thereby causing display mura called gravity defect.
As a method of solving such a problem, one can conceive a method in which the density of the number of the above-described columnar spacers is reduced so as to keep the substrates parallel even with a weak load such as by the vacuum press method. However, when the density of the number of columnar spacers is reduced, there will be a problem in the uniformity of the panel particularly in the case of a large-size liquid crystal display, so that the method cannot be adopted.
On the other hand, one can conceive a method of reducing the hardness of individual columnar spacers, a method of reducing the size of the columnar spacers themselves, or the like method. However, when such a method is adopted, the amount of plastic deformation will typically be large, thereby raising a problem such as generation of display defect when a local load is applied, for example, in the case of a pressure resistance test such as finger pressing test.
Here, no prior art documents regarding the present invention have been found.